About the cover
A magnetic model of the Sun before a solar eruption produced by an ejected magnetic rope (top/blue) using data from the Helioseismic and Magnetic Imager of the NASA Solar Dynamics Observatory mission. Coronal mass ejections are large-scale eruptions in the solar atmosphere that consist of a giant cloud of solar plasma embedded in a magnetic field. They have the potential to produce solar storms here on Earth that can damage artificial satellites and disrupt ground-based power generation. Using observations of the photospheric magnetic field made during the four days leading up to the coronal mass ejection of 13 December 2006, together with numerical modelling, Tahar Amari et al. show that the physical mechanism responsible for such ejections is best explained as the appearance and the later ejection of a twisted rope’ of magnetic flux. Cover: Tahar Amari/ CNRS-Ecole Polytechnique. France.